1. Field of the Invention
The present invention relates to conductive coils for use in inductors, transformers and other electrical or electronic devices.
2. Description of Related Art
Coils may be used as circuit elements in a wide variety of electrical and electronic devices, and are used extensively as windings for inductor/transformers. Conventional multi-turn and thick single turn coils consist of multiple pieces of conductive material soldered together in series or in parallel. Each piece of conductive material requires a solder joint to be electrically connected into a continuous conductive path. Circuit elements with solder joints require expensive and time consuming soldering steps that significantly increase manufacturing costs. In addition, a current passing through a solder joint encounters significantly more electrical resistance at the solder-substrate interface than a jointless conductive path. As electronic devices are reduced in size, the solder joints become increasingly difficult to bond, and each solder joint along a conductive path becomes a potential source of defects. These defects may ultimately cause failure of the electronic device. Even a solder joint that is defect-free during production can become a likely candidate for failure once the electronic device is exposed to moisture, vibration and temperature extremes.
It would be desirable in the art to provide a winding that does not require solder joints for assembly. This winding would be easier to manufacture, exhibit fewer manufacturing defects, and be more reliable in operation. The present invention addresses these requirements by providing a continuous, conductive coil for use in electronic devices such as transformers, circuit boards and the like. The coils of the present invention are made of a continuous length of a conductive material, and require no solder joints to create an efficient, low-loss winding for transformers and other electronic devices. The present invention includes designs for both single turn and multi-turn coils.
Single Turn Coils
Single turn coils are widely used as windings in inductors/transformers and other electronic devices. To reduce power loss when designing windings, the length of the winding is generally minimized, and its cross-sectional area or thickness increased. Increases in the thickness or the cross-sectional area of the turns in windings reduce power losses in the finished device, but these thick materials are difficult and expensive to manufacture. Thick pieces of metal (typically copper) in a finished device are also difficult to electrically insulate.
Conventional thick, single turn multi-turn wound coils consist of multiple pieces of conductive material. Each piece of conductive material requires a solder joint to be electrically connected into a continuous conductive path. To eliminate the need to join two thinner turns of conductive material to make a thick single-turn wound coil, one embodiment of the present invention is a conductive element that may be folded into a single turn. This conductive element is made of one continuous piece of a conductive material and includes a first terminal, a second terminal and a continuous conductive path between the first terminal and the second terminal. In one embodiment, the conductive path includes a first curve, a second curve, and a foldable hinge region between the first curve and the second curve. In certain embodiments, within the first and second curves, apertures may be sized to accept a specific magnetic core configuration that provides a flux path for the magnetic field generated by the winding.
After the coil element is shaped for a particular application, the conductive elements are insulated by laminating the element between at least two layers of relatively thin sheets of an insulative material. The insulating layers create a highly reliable seal that ensures high voltage isolation between the windings. In addition, the seal prevents moisture contamination when an electronic assembly that includes the winding is exposed to a high pressure xe2x80x9cwater-washingxe2x80x9d processes during manufacture.
Following the lamination step, the conductive element is folded at the foldable hinge region to form a single-turn winding. The conductive element is folded such that the current travels around each curve of the conductive path in a single direction. The turns need not be oriented in any specific way following the folding step, but for improved performance the first curve should lie in a first plane and the second curve should lie in a second plane. The first plane and the second plane are preferably substantially-parallel to one another, and the first turn and the second turn overlie one another. After the folding steps are completed, the curves of the winding may optionally be adhered to one another using a suitable adhesive. The completed winding may then be associated with a magnetic core that fits inside the apertures.
2-Turn Coil
Another embodiment is a coil element that may be folded into a conductive coil with two turns. The coil element is made of a continuous strip of a conductive material and includes a first terminal, a second terminal, and a conductive path between the first terminal and the second terminal. The conductive path includes a first turn connected to the first terminal, a second turn connected to the second terminal, and a foldable hinge region between the first and the second turns.
After the coil element is shaped for a particular application, the element is laminated in layers of an insulative material as described above. The insulative material may be removed from the apertures inside the first and second turns to create an opening to accept a magnetic core.
The laminated coil element may be folded about the foldable hinge region to form a continuous conductive coil with turns in substantially parallel planes, although such an orientation is not required. For example, the coil includes a first terminal connected to a first turn in first plane. A second turn is in a second plane substantially parallel to the first plane. The first turn and the second turn are connected via the foldable hinge region, which spans the first and second planes. The second turn connects to a second terminal. The first and second turns are positioned adjacent one another in the parallel planes, and substantially overlie one another. The turns may then optionally be adhered to each other to reduce noise and vibration in the coil under high current conditions. Because each turn is individually sealed, the adhesive used in adhering them need not be relied upon to provide a moisture-impervious seal.
Multi-turn Coils
To make a coil with more than two turns, the basic coil elements described above may be linked in series to form a coil element with multiple turns. The conductive coil element used to make a multi-turn coil is a continuous conductive strip including a first terminal, a second terminal, and a conductive path between the first and the second terminal. The conductive path includes an arrangement of conductive regions linked together in series by a connector region between each conductive region. The conductive regions have at least one and no more than two turns. If a conductive region has a single turn, the turn in that conductive region is connected to an adjacent conductive region in the series by a connector region. If a conductive region has two turns, the turns in that conductive region are connected to each other by a foldable hinge region. If two adjacent turns in the series are connected by a connector region, a current travels around each turn in the same direction. If two adjacent turns in the series are connected by a foldable hinge region, and the turns are assumed to lie in the x-y plane, a current travels in opposite directions relative to the z axis in each turn on either side of the foldable hinge region. This turn arrangement ensures that a current will flow in the same direction around the turns of the folded, completed coil.
Once the conductive element is shaped with a primary conductive region and the desired number of secondary conductive regions, the conductive element may be insulated as described above. The laminated conductive element may then be folded about the connector regions and foldable hinge regions to create a coil with a desired number of turns in a specific arrangement.
If the conductive element requires 5 or more turns (n greater than 4), a specific folding protocol is preferred. First, the paired turns in each second conductive region are folded at the junction of their respective foldable hinge regions so that the turns in each pair substantially overlie one another. The connector region linking the first conductive region and the nearest second conductive region is then folded about its first end until the connector region lies above or behind the foldable hinge region in the first conductive region. Each successive connector region closest to the first conductive region is then folded about the foldable hinge region of the first conductive region.
After this step is completed, all turns in each second conductive region lie in adjacent parallel planes. Finally, the turns in the first conductive region are bent and folded about their foldable hinge region such that all the turns in the conductive element overlie one another. Although a specific orientation is not required, for optimal performance the turns should substantially overlie one another in parallel planes and form a multi-turn coil.
The turns of the coil may then optionally be bonded together with an adhesive. The resultant coil may then be associated with a core and other winding elements to form a transformer or incorporated into any electronic circuit or device.
The continuous multi-turn coil of the present invention requires no solder joints. This reduces time-consuming soldering steps, which would be expected to significantly reduce manufacturing costs. The reduced number of soldering steps means that the coils of the present invention may be made smaller and with fewer manufacturing defects than conventional devices. The reduced number of soldering solder joints also makes the coils of the present invention more reliable under demanding environmental conditions.
The fabrication and sealing process for making the coil elements of the present invention is highly repeatable. Each turn of the coil element may be shaped for use in a wide variety of transformers or other magnetic coil component configurations. A large number of transformers or magnetic coil components may be constructed from a limited number of winding configurations simply by coupling the winding to other winding elements such as, for example, a printed circuit board or another winding.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and the drawings, and from the claims.